ABSTRACT The proposed study is in direct response to two gaps in school-based aggression prevention programming and research. First, there are very few culturally-sensitive relational aggression prevention programs with documented success among high-risk urban minority girls and their classmates despite clear evidence that these behaviors negatively impact girls' social and emotional health and the broader classroom environment. Second, when such programming is conducted, it is often led by externally funded facilitators in the context of a research grant, which does not equip school staff with skills to run the program and makes it exceedingly difficult for schools to sustain programming efforts after research funding has ended. This is particularly concerning in urban schools where aggressive students are often referred to counselors who typically do not have the training and/or resources available for a proactive or systematic response. To address these gaps, this proposal is grounded in the Friend to Friend Program, which was initially designed through an iterative partnership-based research process uniquely for 3rd-5th grade minority relationally aggressive girls in urban schools. Friend to Friend was proven effective through a clinical trial for decreasing relational aggression and improving problem-solving and leadership of relationally aggressive girls with effects maintained one year later, and for producing broader positive effects on aggression and student-teacher relationships for the classmates of the aggressive girls. In the trial, Friend to Friend was conducted by research staff, and no schools continued the program when the study ended. Therefore, preliminary studies were conducted to translate Friend to Friend from researcher-led to school-led with coaching from the research team to address the imperative need to build the capacity of schools to run programs on their own in an effective and sustainable way. As such, the primary goal of this proposal is to examine for the first time the effectiveness of Friend to Friend with Coaching, as conducted by teachers and counselors with active coaching from the research team. Through a cluster randomized control trial including 40 urban schools, 20 schools will be randomly assigned to the F2F with Coaching intervention and 20 control schools will follow standard school practice of referring aggressive youth to the counselor. We will examine indicated and universal effects for students and self-efficacy of school staff for intervening with relational aggressors. In addition, theoretical advances will be made by exploratory goals related to understanding mediators and moderators of program success. Further, we will also explore the effectiveness of Friend to Friend with Coaching the following year when minimal coaching is provided, as well as the facilitators and barriers of program adoption by school staff. Collectively, this study will demonstrate the effectiveness of school-led Friend to Friend with Coaching and the ways in which it works for improving the social and emotional health of relationally aggressive girls and their classmates, and the study will also inform considerations for sustainable program adoption and large scale dissemination.